1. Field of the Invention
The present invention relates to artificial lift for hydrocarbon wells. More particularly, the invention relates to gas operated pumps for use in a wellbore. More particularly still, the invention relates to a gas operated pump having a removable valve insertable in a housing with fluid pathways in the housing that operate in conjunction with the valve.
2. Description of the Related Art
Oil and gas wells include a wellbore formed in the earth to access hydrocarbon-bearing formations. Typically, a borehole is initially formed and thereafter the borehole is lined with steel pipe, or casing in order to prevent cave in and facilitate the isolation of portions of the wellbore. To complete the well, at least one area of the wellbore casing is perforated to form a fluid path for the hydrocarbons to enter the wellbore. In some instances, natural formation pressure is adequate to bring production fluid to the surface for collection. More commonly however, some form of artificial lift is necessary to retrieve the fluid.
Artificial lift methods are numerous and include various pumping arrangements. One common pump is a gas operated pump, as shown in FIG. 1. FIG. 1 is a section view of a wellbore with a gas operated pump disposed therein. The pump 30 is located adjacent perforations in the wellbore 10. The pump operates with pressured gas injected from a high pressure gas vessel 24 into a gas supply line 80 to a valve assembly 40 disposed in a body of the pump 30. The valve assembly 40 consists of an injection control valve 70 for controlling the input of gas into a accumulation chamber 34 and a vent control valve 90 for controlling the venting of gas from the chamber 34. Operational power is brought to the valve assembly 40 by input lines 75, 77. The pump 30 has a first one-way valve 36 at the lower end 38 of the chamber 34. An aperture 37 at the lower end 38 of the chamber permits formation fluid to flow through open valve 36 to enter the chamber 34. After the chamber 34 is filled with formation fluid, the vent control valve 90 closes and the injection control valve 70 opens. Gas from the gas supply line 80 is allowed to flow through the open injection control valve 70 into the chamber 34. As gas enters the chamber 34, gas pressure forces the formation fluid downward, thereby closing the first one-way valve 36. As the gas pressure increases, formation fluid therebelow is urged into outlet 42 and opens a second one-way valve 47. Fluid enters the valve 47 and travels along passageway 32 and into the tubing string 20. After formation fluid is displaced from the chamber 34, the injection control valve 70 is closed, thereby restricting the flow of gas from the high pressure gas vessel 24.
Hydrostatic fluid pressure in the passageway 32 acts against second one-way valve 47, thereby closing the valve 47 and preventing fluid from entering the chamber 34. The vent control valve 90 is opened to allow gas in the chamber 34 to exit a vent line 100 into an annulus 22 formed between the casing 12 and the tubing string 20. As the gas vents, the gas pressure decreases thereby reducing the force on the valve 36. At a point when the formation fluid pressure is greater than the gas pressure in the chamber 34 the valve 36 opens thereby allowing formation fluid to once again fill the chamber 34. In this manner, a pump cycle is completed. As the gas operated pump 30 continues to cycle, formation fluid gathers in the tubing string 20 and eventually reaches the surface of the well for collection.
U.S. Pat. No. 5,806,598 to Mohammad Amani, incorporated herein by reference in its entirety, discloses a method and apparatus for pumping fluids from a producing hydrocarbon formation utilizing a gas operated pump having a valve actuated by a hydraulically actuation mechanism. In one embodiment, a valve assembly is disposed at an end of coiled tubing and may be removed from the pump for replacement.
The conventional pumps illustrated in FIG. 1 and described in the ""598 patent suffer from problems associated with size limitations in downhole pumps. These valve assemblies for a gas operated pump have an internal bypass passageway for injecting gas into the chamber. The internal bypass passageway must be a large enough diameter to facilitate a correct amount of gas flow into the chamber. These internal structures necessarily make the valve large and bulky. A bulky valve assembly is difficult to insert in a downhole pump because of space limitations in a wellbore and in a pump housing.
There is a need, therefore, for a gas operated pump having a valve assembly that is less bulky. There is a further need for a gas operated pump with a removable valve that does not include a bypass passageway.
The present invention generally provides a gas operated pump having a removable and insertable valve. In one aspect, the invention includes a pump housing having a fluid path for pressurized gas and a second fluid path for exhaust gas. The fluid paths are completed when the valve is inserted into a longitudinal bore formed in the housing.